Following decades of improvement in Southern California, progress has tapered off recently in reducing ozone, which inflames the lungs and triggers asthma attacks and other health problems. The number of bad air days have gone up the last two consecutive years, with the region violating federal health standards for ozone on 145 days last year, up from 132 days in 2016 and 113 in 2015.

Source: Los Angeles Times April 30, 2018 22:07 UTC